Diameter of an atom: 10-10 m
Diameter of Earth: 1.2742 x 107 m
Thickness of a strand of human hair: range from 17 x 10-6 m to 181 x 10-6 m
Length of a bus: 14 m
Diameter of a pin head: 1.5 x 10-3 m
Category: Pure Physics
Describe the use of Fleming’s left-hand rule to determine the direction of the force on a current-carrying conductor cutting through the magnetic field of a magnet.
Applying Fleming’s left-hand rule, the thumb, the index finger, and the middle finger on the left hand are positioned in such a way that they are pointing perpendicular to one another. The thumb will point in the direction of the force, the index finger will point in the direction of the magnetic field, while the middle finger will point in the direction of the conventional current flow.
This rule is also known as the Motor Rule. It is used in situations where electrical energy is converted to mechanical energy, similar to the energy conversion in a motor.
Define electrostatic charging by induction.
It is a process in which electrical charges are redistributed in a neutral body by bringing an electrically charged object near to it.
Note: This type of induction is most effective in electrical conductors, but can also happen in some electrical insulators.
Better still, test it out yourself! 🙂
Explain, in terms of forces, how a speed-time graph change.
Initially, the car’s speed is increasing. This causes the frictional forces to increase. With the forward driving force remaining constant, the resultant force acting on the car will be decreasing.
Since resultant force = mass x acceleration, with a decreasing resultant force, and constant mass, acceleration will be decreasing. This is represented by the decreasing gradient of the speed-time graph.
Eventually, the forward driving force will be equal to frictional forces. When this happens, resultant force acting on the car will be zero, so acceleration will be zero, and the car will be moving at constant speed. This is represented by the horizontal portion of the speed-time graph.
Explain why the fuse and switch are connected to the live wire.
A live wire carries a high voltage and carries current from the electrical plug to the appliance.
The switch connected to the live wire will ensure that the appliance is at zero voltage every time the appliance is switched off, making the appliance safer to use.
The fuse connected to the live wire will ensure that high current flow to the appliance will immediately be cut off, preventing damage to the wirings and appliance due to the high current flow.
Suggest why an electrical appliance with a 2-pin plug is still safe to use.
This appliance is missing an earth wire, but it most likely has double insulation.
Appliances with double insulation have their internal parts and wirings completely insulated from the outer casing, and the outer casing will be made of an electrical insulator, eg plastic.
This means that, even if a live wire touches the casing, it will not become “live”, hence it will be safe to use even without an earth wire.
Note: Appliances with double insulation will have this symbol:
Can a charged insulator transfer its charges to a neutral conductor when they touch?
The short answer is no.
The insulator can be charged via electrostatic charging by friction, but not by electrostatic charging by induction. The charges do not travel easily from the insulator to the conductor or vice versa, simply by putting them in contact.
The electrons in the insulator are not delocalised, hence they are not able to move freely within its own body or cross over to another body to induce a charge.
Examples:
Answer is A
Answer is D
Why does an echo fill an empty room, but not one that is fully furnished?
In an empty room, the hard and solid walls, floors and ceilings act as good reflectors of sound, so the sound waves reflect repeatedly off these surfaces, creating echo.
In a fully furnished room, there are usually soft, hollow surfaces, like the fabric sofa; the thick curtains; the wardrobe, etc, that act as good absorbers of sound. This reduces the effect of echo.
How is lightning formed?
In a storm cloud, water droplets are brought upwards in an updraft within the storm clouds. The droplets cool and freeze into hail and smaller ice particles as they rise upwards. The heavier hail particles that formed then fall back downwards, rubbing against the rising small ice particles.
Electrostatic charging by friction occurs, with the hail particles gaining electrons from the small ice particles. The heavier hail particles, which have become negatively charged, gathered at the bottom part of the storm clouds, while the lighter small ice particles, which have become positively charged, gathered at the top part of the storm clouds.
Electrons near the ground are repelled by the negatively charged bottom of the storm clouds, moving deeper into the ground, resulting in the objects on the surface of the ground becoming positively charged. As the negative charges build up at the bottom of the clouds, surrounding air particles are ionised, sending stepped leaders towards the ground. At the same time, the positively charged objects on the ground also ionise the air particles around them, sending streamers upwards towards the clouds.
When a particular stepped leader and streamer meet, a path is established, and the huge potential difference between the cloud and the object results in a massive current flow.
This huge current flow produces an enormous amount of heat, up to 30 000 deg C, which appear to us as the brilliant white-blue flash of a lightning flash.
Pressure in a syringe
The work done at the barrel is equal to the work done at the nozzle.
Word Done = Force x Distance.
The force at the barrel > the force at the nozzle, so for equal work done,
distance moved by water leaving barrel per second < distance moved by water leaving the nozzle per second.
This results in a greater speed of the water leaving the nozzle.
Alternative Answer:
Volume of water leaving the barrel per second = Volume of water leaving the nozzle per second.
The cylindrical volume = Base area x distance moved by the water.
Since base area of barrel > base area of nozzle, so for equal volumes,
distance moved by water leaving barrel per second < distance moved by water leaving nozzle per second.
This results in a greater speed of the water leaving the nozzle.